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Yellow Rattle

Written by John James, posted on Thursday, June 14, 2018

Currently flowering at the southern end of New Walk and on the Dean's Ham is a relatively inconspicuous but important yellow flower. This is Yellow Rattle (Rhinanthus minor) a member of the Orobranchaceae plant family most of which are parasitic in nature.

This is an interesting native grassland annual which we are encouraging to grow in our wild flower areas, as it is hemi-parasitic on the grass and legume plants. This means that it is parasitic on the grasses and and whilst being capable of carrying out its own photosynthesis it is dependent upon the host grasses for additional supplies of carbohydrates and minerals. By drawing nutrients from surrounding vegetation it impedes its growth and increases the chances of other wild flowers being able to flourish. Because of this it is the enemy of farmers trying to maximise the yields of grass for animal feed but is the friend of those trying to grow wild flower meadows for habitat improvement and species diversity.

The common name derives from the flower colour and the inflated bladder-like seed pod which develops and rattles once the seeds and bladder dry out.

This rattling noise indicates that the plant is ready to drop its seed and, as it is an annual, it is important that we manage the areas to maximise the chances of the Yellow Rattle spreading its own seed. Because of this we cut the meadow areas in August with a sickle bar mower and then leave the cut vegetation to dry out and drop its seeds for a minimum of one week before clearing away the cut grass and flowers. It is important that we remove the cut vegetation in order to prevent the build up of nutrients and to stop it smothering young seedlings as they develop.

The seeds of the Yellow Rattle lie dormant over the winter before germinating in the spring after a period of winter chilling.